The synthesis of preferred polybenzimidazole based high performance fibers requires the selective polymerization of 2,3,5,6-tetraaminotoluene (“TAT”) with various substituted and unsubstituted aromatic diacids, such as 2,5-dihydroxyterephthalic acid (“DHTA”). This requires the synthesis and subsequent condensation polymerization of a 1:1 complex between the diacid and the tetraamine. The ratio of diacid to tetraamine must be as close to 1:1 as possible to achieve high molecular weight. A critical polymer property is intrinsic viscosity. Only material with sufficiently high intrinsic viscosity (i.e., high molecular weight) is suitable for the production of a high tensile strength fiber.
A commercially viable process producing the monomers of fiber-grade purity and in a form allowing for the production of high molecular weight polymer requires a high space time yield process for the synthesis of a 1:1 complex between diacid and tetraamine. A need thus remains for a process for the production of a suitable TAT-diacid monomer complex that can be polymerized to a high molecular weight polymer material for producing high-performance fibers, wherein the complex is formed from a stable precursor without isolation of intermediates.